anybody experienced in the veterinary field who may be able to provide some insight?

So our dog Cody has a vet appt tomorrow first thing in the morning. Back in october, I took hi. To the vet for what felt like a cyst in his neck. Small, but I was still concerned. They gave a us a few ideas, but weren't really sure, he was tested for Lyme disease because we had done some hiking during the summer. He was negative. So they put him on antibiotics (ciptro) for 10 days.it went away, then came back. We took him back and they suggested maybe the dosage wasn't enough to fully remove what ever was causing it from his body, so he was put back on antibiotics (amoxicillon) during the first two weeks of the meds, it grew and his face really swelled up but then it cleared up and went away. But then when we finished the medication, it came back, when it came back it felt like two little cysts, and they started coming through the skin and puss in out. So we brought him back, again and finally surgery was done and they cleared his throat, it seemed to be growing in the area where saliva builds up (the vet had explained all this to me but I didn't really understand to much of it). We brought him back 2 weeks after the surgery for his stitches to be removed and they said he should be good. We'll here we are back to square one. His neck blew up again and hes going back tomorrow. My question is if you are a vet and if you have seen this kind of thing before? I'm not trying to get a diagnosis here I'm really just curious on some opinions of what this could possibly be?